Mark Bullen, RNZ chief technology and operations officer, said the maintenance was "critical". Photo: RNZ / Diego Opatowski
RNZ and a range of other stations' AM broadcasts went off air on Friday, and the unusual daytime disruption is likely to last a week.
A mast in the West Auckland suburb of Henderson will be shut off during work on guy wires between 9.10am and 4.50pm each day.
Guy wires are cables used to stabilise tall structures. The mast in Henderson was first installed in the 1930s, and has been in continuous use since then.
Mark Bullen, RNZ chief technology and operations officer, said the maintenance was "critical".
"The mast is responsible for RNZ National's AM transmission for the Auckland region (AM 756) as well as a range of AM broadcasters in Auckland - 531PI, Parliament / Southern Star, Radio Apna, Radio Ake, NZME Gold AM, SENZ.
"RNZ regularly maintains its masts and sites and typically schedules overnight outages where possible to reduce overall disruption. However, due to the intricate process and the nature of the work required this week, it must be done during daylight hours for safety reasons.
The work began on Wednesday, and was expected to take "up to seven days'".
"We acknowledge the disruption this has on our clients and their audience, but we can assure it's urgent and are working swiftly to secure normal programming resumes for broadcasters," Bullen said.
"A more detailed and technical explanation has been provided to the broadcasters affected."
While not carrying the same audio fidelity as FM signals, AM can travel much further.
The site in Henderson was chosen "because the location was widely considered appropriate for radio transmission due to the extent of open, flat land surrounding" according to a document on the Auckland Council website.
It began operations in 1934, the same year the first purpose-built public radio building on Shortland Street, which was later home to TVNZ.